Hydrogen permeation window is a candidate not only as the tritium recovery device from liquid lithium, but also as the hydrogen isotopes monitor for molten lithium because hydrogen permeation rate is dominated by hydrogen concentration. In this study, changing tritium concentration in lithium, tritium permeation through iron window contacting with tritium was quantified by ionization chambers. As a result, measurable amount of tritium permeated the window even though tritium concentration in lithium was in the order of wppb. The amount of tritium permeation increased as tritium concentration in lithium increased. Iron window is hopeful as tritium monitor for liquid lithium.